Question

When a jet plane travels faster than sound what happens?

Answer 1

The phenomenon you're talking about is called Sonic Boom. When the airplane exceeds the speed of sound, its sound waves keep on piling up behind it. When these waves pile up to an extent, they result in an explosion, thus creating a booming sound!

Answer 2

We will see that plane pass away first and and then we will hear the sound

Let me give you my example
I use to see jet crafts every day going from west to east above my house

When I hear the sound and i rush to see it, I found the sound coming from west side, but on searching the sky I found plane in eastern sky while sound still comes from west

Hope you got my point